As the trial continues for William Darfur, the then-husband of Jennifer Hudson’s sister who is accused of murdering Jen’s mother, brother and nephew, more details have emerged…not in his favor. A woman took the stand to testify she’d been sleeping with William while he was married to Jen’s sister, provoking Jen’s “most animated reaction yet.” More details below.

Marisa Mendez

(RO) – Before he allegedly gunned down Jennifer Hudson’s mother, brother and nephew, William Balfour was cheating on her sister, according to a witness who testified in his triple murder trial on Thursday.

Diana Grant told the Chicago courtroom that she met the defendant in 2007 through friends, she found out Balfour was married to Julia Hudson a few months later but says she was already in love with him and they continued to date, reported the Chicago Tribune.

The revelation of the extra-marital affair caused the most animated reaction yet from the Oscar winner and her sister, who sat whispering heatedly while they heard how Grant met Balfour – whom she nicknamed “Flex” and “Baby” – at hotels for illicit hookups, bought him clothes, and even put up with him dating other women.

As RadarOnline.com previously reported, Jennifer broke down in tears on Monday when she told the Chicago courtroom how she had begged Julia not to marry Balfour, and did not find out that her sister had gone through with it until months later.

Balfour faces three counts of first-degree murder, aggravated kidnapping and home invasion in the 2008 deaths of Jennifer and Julia Hudson’s mother Darnell Hudson Donerson, 57; brother Jason Hudson, 29; and Julia’s son Julian King, 7.

Grant told jurors how William slept at her apartment the night before the murders, but instead of wanting to have sex with her, he left around 6 a.m. when it was still dark. Prosecutors allege that around three hours later he fatally shot Darnell and Jason in a revenge attack against Julia, then snatched young Julian from the house and drove him to the West Side of Chicago to kill him.

Balfour’s mistress said she repeatedly called and texted him that day, he finally answered at 4 p.m. and promised he would call her back but never did. Instead he went to another girlfriend’s house – whom she was oblivious of – where he was later arrested.

A key part of Grant’s testimony tied the suspected killer to a house on the same block of the Hudsons’ home on Yale Street, where a woman lived who he had allegedly asked to be an alibi to the murders.

Also testifying during Thursday’s proceedings was James Payton, who backed up the prior allegations that Jason Hudson was a drug dealer.

“While he was waiting for his disability checks, he’d sell a little bit of drugs,” said an emotionally distraught Payton, who was Jason’s best friend and once dated the former American Idol contestant.